| 摘要 |
PURPOSE:To measure the moving speed and the orientation of an automobile, for example, mounting a GPS receiver accurately by narrowing the frequency bandwidth of a control system thereby enhancing the the synchronization accuracy. CONSTITUTION:A despread spectrum processing section 13 demodulates a pseudo noise signal using an intermediate frequency signal received through an antenna 11 and a receiving/processing section 12. An oscillator 20 generates a sine wave of same frequency as the Doppler shift frequency and a Doppler shift frequency removing section 14 multiplies the sine wave signal by a demodulated signal received from the section 13 thus removing the Doppler shift frequency component. A phase difference detecting section 18 detects the residual Doppler shift frequency as a phase difference and a frequency control section 19 controls the phase difference to zero. Since the residual Doppler shift frequency contains only the operation error of offset frequency, the frequency bandwidth of the control system is narrowed. Subsequently, a speed/direction data is outputted through a data demodulating section 15 and a receiving position operating section 16. |
